Shielding techniques for noise reduction in surface electromyography signal measurement and related systems and methods

ABSTRACT

Techniques for shielding wearable surface electromyography (sEMG) devices are described. According to some aspects, an sEMG device may comprise amplification circuitry comprising at least a first differential amplifier and at least two sEMG electrodes electrically connected to the amplification circuitry. The device may further comprise at least one auxiliary conductor not electrically connected to the amplification circuitry, wherein the at least one auxiliary conductor is configured to be electrically coupled to a wearer of the wearable device, and an electromagnetic shield surrounding the wearable device at least in part and electrically connected to the at least one auxiliary conductor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/677,574, filed May 29, 2018, titled “Techniques for Shielding Surface Electromyography Signals and Related Systems and Methods,” and U.S. Provisional Patent Application No. 62/696,242 filed Jul. 10, 2018, titled “Shielding Techniques for Noise Reduction in Surface Electromyography Signal Measurement and Related Systems And Methods,” each of which is hereby incorporated by reference in its entirety.

BACKGROUND

Surface electromyography (sEMG) is a process that involves the detection of electrical activity produced by one or more groups of muscles, at rest and/or during activity. High quality sEMG signals are typically acquired from wet electrodes in a laboratory setting using skin preparations that require application of a gel or paste at the electrode-skin interface to improve the conductivity between the skin and the electrodes. In wireless communication applications, shielding is typically used to reduce radio-frequency interference and it is normally implemented by covering all or portions of the circuit with shielding material connected to the ground plane.

SUMMARY

According to some aspects, a wearable device is provided comprising amplification circuitry comprising at least a first differential amplifier, at least two sEMG electrodes electrically connected to the amplification circuitry, at least one auxiliary conductor not electrically connected to the amplification circuitry, wherein the at least one auxiliary conductor is configured to be electrically coupled to a wearer of the wearable device, and an electromagnetic shield surrounding the wearable device at least in part and electrically connected to the at least one auxiliary conductor.

According to some aspects, a method of attenuating noise in a wearable device is provided, the wearable device comprising amplification circuitry, at least two sEMG electrodes electrically connected to inputs of the amplification circuitry, and an electromagnetic shield surrounding the wearable device at least in part, the method comprising electrically coupling the at least two sEMG electrodes to a wearer of the wearable device, and electrically coupling the electromagnetic shield to the wearer without electrically coupling the electromagnetic shield to the amplification circuitry except via the wearer and via air between the electromagnetic shield and the amplification circuitry.

It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

BRIEF DESCRIPTION OF DRAWINGS

Various non-limiting embodiments of the technology will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale.

FIG. 1 is a schematic diagram of components of an sEMG system in accordance with some embodiments of the technology described herein;

FIG. 2 illustrates a wristband having sEMG sensors arranged circumferentially thereon, in accordance with some embodiments of the technology described herein;

FIG. 3 illustrates a user wearing the wristband of FIG. 2 while typing on a keyboard, in accordance with some embodiments of the technology described herein;

FIG. 4 depicts an illustrative amplifier of an sEMG device, according to some embodiments;

FIG. 5 depicts an illustrative amplifier of an sEMG device in which a shield mitigates interference produced by sources of external noise, according to some embodiments; and

FIGS. 6A-6D depict illustrative cross-sectional views of sEMG devices that include a shield surrounding electronics of the sEMG device, according to some embodiments.

DETAILED DESCRIPTION

Obtaining consistent high-quality sEMG signals using sEMG electrodes and conventional signal conditioning and processing techniques is challenging, in part due to the low voltages produced by muscle fibers. Moreover, obtaining high-quality sEMG signals from dry sEMG electrodes is generally more challenging than with wet sEMG electrodes, because wet sEMG electrodes generally have a lower impedance conductive path between the electrode and the skin via an intervening gel. With dry sEMG electrodes, however, there may be various low conductivity materials between the electrode and the skin, such as air, body hair and/or moisture, resulting in inconsistent electrode signals that may exhibit considerable noise. For applications that require near real-time analysis of sEMG signals with dry electrodes, the acquisition of consistent high-quality signals with reliable devices is important, both from a user experience perspective and from a development perspective. As referred to herein, sEMG signals are signals produced by one or more sEMG electrodes, and are typically produced by the electrodes in response to electrical signals produced by one or more muscles or groups of muscles.

The inventors have recognized and appreciated that sEMG signals are low amplitude in nature (e.g., in the range of several μV to several mV) and particularly susceptible to external noise sources, which can capacitively couple through the air to a circuit containing sEMG electrodes. For instance, external noise may couple through the air to inputs of an sEMG data acquisition system, particularly in the case of high impedance inputs. External sources of noise may include, for example, AC power lines and AC-powered devices, which may produce sources of 50 Hz or 60 Hz noise. While the capacitance of the air is comparatively small (e.g., on the order of femtofarads), the voltages of sEMG signals may be sufficiently low such that even a heavily attenuated source of external noise can produce a signal that interferes with accurate measurement of the sEMG signals.

The inventors have further recognized and appreciated that conventional approaches to shielding circuits function poorly in sEMG devices (that is, a device that includes one or more sEMG electrodes). For instance, conventional shielding techniques typically place a conductor around a circuit and directly connect the conductor to the circuit ground or some other well-defined potential. It has been observed by the inventors, however, that such an approach does not appreciably suppress signals produced within an sEMG device by external sources of noise, and in some cases may even increase the amount of noise in the sEMG signals.

Some embodiments are directed to techniques for suppressing signals produced within an sEMG device by external sources of noise by electrically coupling a shielding structure to the skin of the wearer of a wearable device that includes sEMG sensors arranged thereon. The shielding structure acts to substantially suppress signals produced within an sEMG device by external sources of noise. Such suppression of noise may occur even though the body of the wearer provides a ground that is generally not well-defined, nor necessarily at a stable potential.

FIG. 1 schematically depicts components of an illustrative sEMG system 100, in accordance with some embodiments. System 100 includes a pair of sEMG electrodes 110, which may include any combination of wet and/or dry sEMG electrodes. In some embodiments, electrodes 110 may be arranged as a portion of a wearable device configured to be worn on or around part of a user's body. For example, in one non-limiting example, a plurality of sEMG sensors including sEMG electrodes (e.g., electrodes 110) are arranged circumferentially around an adjustable and/or elastic band such as a wristband or armband configured to be worn around a user's wrist or arm. Alternatively, at least some of the sEMG sensors may be arranged on a wearable patch configured to be affixed to a portion of the user's body.

In some embodiments, the sEMG electrodes may be minimally invasive and may include one or more conductive components placed in or through all or part of the dermis of the user. In at least some cases of the above-described arrangement, the resulting EMG signals may not, in a strict technical sense, be considered “surface” EMG signals. Nonetheless, reducing external sources of noise is also a fundamental challenge for minimally invasive EMG recordings.

In one implementation, sixteen sEMG sensors including sEMG electrodes are arranged circumferentially around an elastic band configured to be worn around a user's lower arm. For example, FIG. 2 shows sEMG sensors 204 arranged circumferentially around elastic band 202. It should be appreciated that any suitable number of sEMG sensors having any suitable number of sEMG electrodes (including wet and/or dry sEMG electrodes) may be used and the number and arrangement of sensors/electrodes may depend on the particular application for which the wearable device is used. For example, as shown in FIG. 2, some of the sEMG sensors 204 include two sEMG electrodes, whereas others of the sEMG sensors 204 include three sEMG electrodes, with the middle of the three electrodes being a ground electrode. The ground electrode may be included on one or more of the sEMG sensors 204 to, for example, further bias the skin potential and/or to filter out noise. Although the schematic diagrams in FIGS. 1, 4 and 5 illustrate only two or three electrodes being connected to an amplifier, it should be appreciated that for sEMG sensors 204 in which three (or more) electrodes are used, a corresponding number of connections between the electrodes and the amplification circuitry would be included. In one example application of the technology described herein, FIG. 3 shows a user 306 wearing elastic band 302 on hand 308. In this way, sEMG sensors 304 may be configured to record sEMG signals as a user controls keyboard 312 using fingers 310.

Surface potentials recorded by sEMG electrodes are typically small and amplification of the signals recorded by the sEMG electrodes is typically desired. As shown in FIG. 1, sEMG electrodes 110 are coupled to amplification circuitry 112, configured to amplify the sEMG signals recorded by the electrodes. The output of the amplification circuitry 112 is provided to analog-to-digital converter (ADC) circuitry 114, which converts the amplified sEMG signals to digital signals for further processing by microprocessor 116. Microprocessor 116 may be implemented by one or more hardware processors. The processed signals output from microprocessor 116 may be interpreted by host machine 120, examples of which include, but are not limited to, a desktop computer, a laptop computer, a smartwatch, a smartphone, or any other computing device. In some implementations, host machine 120 may be configured to output one or more control signals for controlling a physical or virtual device based, at least in part, on an analysis of the signals output from microprocessor 116.

As shown, sEMG system 100 also includes sensors 118, which may be configured to record types of information about a state of a user other than sEMG information. For example, sensors 118 may include, but are not limited to, temperature sensors configured to measure skin/electrode temperature, inertial measurement unit (IMU) sensors configured to measure movement information such as rotation and acceleration, humidity sensors, heart-rate monitor sensors, and other bio-chemical sensors configured to provide information about the user and/or the user's environment.

One illustrative implementation of amplification circuitry 112 shown in FIG. 1 is illustrated in FIG. 4, according to some embodiments. In the example of the sEMG device 400 shown in FIG. 4, sEMG electrodes 441, 442 and 443 (which are, for example, instances of electrodes 110 shown in FIG. 1, and which may include any combination of wet and/or dry sEMG electrodes) are electrically coupled to a user's body 450. Due to the nature of contact afforded by sEMG electrodes, the coupling between each of the electrodes 441, 442, 443 and the body 450 is associated with resistances R_(in+), R_(in0), R_(in−), respectively, and capacitances C_(in+), C_(in0), C_(in−), respectively. The values of these resistances and capacitances may be expected to vary between the electrodes due to, for example, one or more of: variation in skin conditions (e.g., hydration levels, amounts of intervening body hair), differing amounts of physical contact between the respective electrode and skin, and/or manufacturing variations between electrodes 441, 442 and 443.

In the example of FIG. 4, signals sensed by the electrodes 441 and 443 are provided to inputs of the differential amplifier 420, which is powered using a dual power supply with voltage +V_(CC) (423) as a positive supply and voltage −V_(CC) (426) as a negative supply with respect to ground (424). An amplified signal produced by the amplifier 420 is output at 425. Electrode 442 is connected to circuit ground 424. In at least some cases, the connection of electrode 442 to circuit ground 424 may act to bias the body 450; for example, the connection may stabilize the body DC potential at circuit ground.

As discussed above, in some cases external noise sources can couple through the air to sEMG devices. For instance, in the example of FIG. 4, the noise source 410 may couple to the inputs of the amplifier circuit through the air, represented in FIG. 4 by the capacitors 431 and 432 which represent the parasitic capacitance between noise source 410 and inputs of amplifier 420. Unwanted noise may thereby be produced in output 425.

For example, based on the illustrated parasitic capacitances of the air and amplifier inputs from electrodes 441 and 443 shown in FIG. 4, and ignoring the resistances R_(in+), R_(in0), R_(in−) for simplicity, the voltage signals that the noise source 410 produces as input to the amplifier 420 may be expressed as:

$\begin{matrix} {V_{{{in} +},{noise}} = {\left( \frac{C_{air}}{C_{air} + C_{{in} +}} \right) \times V_{noise}}} & \left( {{Eqn}.\mspace{14mu} 1} \right) \\ {V_{{{in} -},{noise}} = {\left( \frac{C_{air}}{C_{air} + C_{{in} -}} \right) \times V_{noise}}} & \left( {{Eqn}.\mspace{14mu} 2} \right) \end{matrix}$ where V_(noise) is the noise signal produced by the noise source 410 (e.g., a 60 Hz signal produced by an AC power cable and/or AC-powered device). Note that the voltages V_(in+,noise) and V_(in−,noise) are voltage signals input to the amplifier 420 in addition to sEMG voltage signals sensed by the electrodes 441 and 443 from the body 450. Moreover, it should be appreciated that in some cases the capacitance of the air may not be identical in each of the above equations due to minor differences in distance between the noise source and the amplifier, but is treated as so for simplicity.

As Eqns. 1 and 2 illustrate, noise signal V_(noise) is attenuated by the air, but since C_(in+) and C_(in−) are generally not equal, V_(in+,noise) and V_(in−,noise) are also not equal. As a result, a differential noise input is produced at the inputs of amplifier 420. In addition, although the capacitance of the air may be on the order of femtofarads, the capacitances C_(in+) and C_(in−) may generally be on the order of nanofarads. As a result, the attenuation factors in Eqns. 1 and 2 may be on the order of 10⁻⁶. For many devices, such a level of attenuation of the noise signal (e.g., resulting in a noise signal of order 1 μV) results in noise far below the level of the signals within the device. However, for sEMG electrode devices the voltages recorded by the electrodes are also generally small (on the order of μV or smaller), so that even the attenuated noise signals are problematic and interfere with the sEMG signals input to the amplifier 420. Moreover, since sEMG devices are often used in environments containing multiple electronic devices (e.g., AC mains devices, computer processors, displays, etc.) multiple sources of such noise can compound this problem.

FIG. 5 depicts an illustrative amplifier 520 of an sEMG device 500 in which a shield 560 is arranged to mitigate interference caused by external noise, according to some embodiments. Shield 560 may be referred to as an “electromagnetic shield” in that it mitigates electromagnetic interference, although it may be appreciated that, in at least some cases, the shield may not interact with both electric and magnetic fields when shielding external sources of interference.

As with the example of FIG. 4, in device 500 an external source of noise 510 produces noise signals V_(in+,noise) and V_(in−,noise) at the inputs to amplifier 520. To reduce the effect of this noise, a shield 560 is arranged between the noise source 510 and the amplifier 520, and is coupled to the user's body 550. Shield 560 produces additional attenuation of the noise signal V_(noise), as described in more detail below. Shield 560 may comprise any suitable conductive material or materials, including, but not limited to, one or more metals and/or alloys (e.g., aluminum, copper, and/or mu-metals), conductive paint (e.g., silver and/or carbon-based paint), conductive fabric (e.g., silver nanowire), conductive polymers (e.g., carbon or graphene filled polylactic acid (PLA)), conductive plastics, conductive rubbers, conductive silicones, or combinations thereof. Shield 560 may also include one or more non-conductive components that may be combined with any one or more conductive components, such as the aforementioned examples.

Based on the illustrated parasitic capacitances of the air (C_(air) and C′_(air)), amplifier inputs from electrodes 541 and 543 shown in FIG. 5, and the capacitance C_(body) representing the coupling of the shield 560 to the user's body 550, the voltage signals that the noise source 510 produces as input to the amplifier 520 may be expressed as:

$\begin{matrix} {V_{{{in} +},{noise}} = {\left( \frac{C_{air}^{\prime}}{C_{air}^{\prime} + C_{body}} \right) \times \left( \frac{C_{air}}{C_{air} + C_{{in} +}} \right) \times V_{noise}}} & \left( {{Eqn}.\mspace{14mu} 3} \right) \\ {V_{{{in} -},{noise}} = {\left( \frac{C_{air}^{\prime}}{C_{air}^{\prime} + C_{body}} \right) \times \left( \frac{C_{air}}{C_{air} + C_{{in} -}} \right) \times V_{noise}}} & \left( {{Eqn}.\mspace{14mu} 4} \right) \end{matrix}$ where once again the resistances R_(body), R_(in+), R_(in0), R_(in−) are ignored for simplicity. Electrode 542 of FIG. 5 is connected to circuit ground 524. In at least some cases, the connection of electrode 542 to circuit ground 524 may act to bias the body 550; for example, the connection may stabilize the body DC potential at circuit ground.

The magnitude of C_(body) may be expected to be on the order of nanofarads, and as such the additional attenuation factor of

$\left( \frac{C_{air}^{\prime}}{C_{air}^{\prime} + C_{body}} \right)$ present in Eqns. 3 and 4 compared with the single attenuation factor in Eqns. 1 and 2 leads to a greater attenuation of the noise at the inputs of the amplifier 520 using the circuit configuration shown in the example of FIG. 5.

It will be appreciated that the parasitic capacitances of the air 531 and 532 may not be identical to one another in all cases due to minor differences in environment between the noise source and the shield but is treated as so in the discussion above for simplicity. Similarly, it will be appreciated that the parasitic capacitances of the air 533 and 534 may not be identical to one another in all cases due to minor differences in environment between the shield and the amplifier, but is treated as so in the discussion above for simplicity.

It will be appreciated that shield 560 may be arranged between noise source 510 and the amplifier 520 in numerous ways, and that shield 560 may have any suitable geometry to enable such an arrangement. In some embodiments, shield 560 encloses (e.g., completely surrounds) the amplifier so that the shield is arranged between the amplifier and the external noise sources. In some embodiments, shield 560 may surround the amplifier so that the shield is arranged between the amplifier and noise sources that may be incident on the amplifier from some directions, but where the shield does not completely enclose the amplifier. It will also be appreciated that shield 560 may completely surround or partially surround an entire sEMG system, such as sEMG system 100 shown in FIG. 1.

For example, in the case of the illustrative sEMG device shown in FIGS. 2 and 3, shield 560 may be implemented as a conductive layer that surrounds the sEMG sensors 204 and/or 304 without the shield being located between the sEMG sensors 204 and/or 304 and the wearer's skin. Such an arrangement may enable attenuation of noise by coupling the shield to the wearer's body in any of various ways, examples of which are discussed below.

In addition, while in the example of FIG. 5 the shield 560 is coupled to the wearer's body via sEMG electrode 545, the shield may in general be electrically coupled to the wearer's body in any suitable way using any number of auxiliary conductors (that is, conductors other than sEMG electrodes connected to one or more amplifier inputs of the device). For instance, the shield may be electrically coupled to the wearer's body via one or more electrodes other than an sEMG electrode and/or via one or more other conductors. In some implementations, an auxiliary conductor may be part of the shield itself.

Shield 560 may be electrically coupled to any suitable part or parts of the wearer's body. In the case of an sEMG device configured to be worn on an arm, for example, the shield may be configured to electrically couple to the same arm, including the ventral and/or dorsal sides of the arm, and/or to other parts of the body (e.g., the other arm). The presence of body hair on surface of the body is a complicating factor for achieving a good electrical contact with the body for surface-mounted electrodes. Electrically coupling the shield to the ventral side of the arm may be advantageous, as the ventral side of the arm typically has less body hair than the dorsal side resulting in a better coupling of the shield to the body. It should be appreciated that a desired or optimal placement of the electrode/conductor connected to shield 560 on a user's body may vary from user to user depending on one or more factors including, but not limited to, density of body hair, type of wearable sEMG device, and user preference.

Although the techniques discussed above in relation to FIG. 1, FIG. 2, FIG. 3, FIG. 4 and FIG. 5 are discussed in the context of differential input amplifiers, it will be appreciated that the shielding techniques described herein can also be implemented with other types of amplifiers, such as single-ended input amplifiers, in place of the differential input amplifier in the above-described examples. As may be noted from Eqns. 3 and 4 above, the amplitude of the noise may be attenuated at each individual input of an amplifier, which may also be the case for amplifiers other than differential input amplifiers.

FIGS. 6A-6C depict illustrative cross-sectional views of sEMG devices that include a shield completely or partially surrounding electronics of the sEMG device (e.g., one or more amplifiers or even an entire sEMG system), according to some embodiments. In the example of FIG. 6A, sEMG device 600 includes a shield 603 that surrounds device electronics 602 and an sEMG electrode 604. Shield 603 extends onto the wearer's body 601 to electrically couple the shield to the body as discussed above in relation to FIG. 5. As a result, the shield 603 attenuates external sources of noise (not pictured) that may couple to aspects of the device electronics 602.

According to some embodiments, shield 603 may include and/or may form part of the housing of sEMG device 600. As non-limiting examples, the shield 603 may comprise a rigid conductor that forms a housing around device electronics 602 and contacts the body 601; the shield 603 may comprise a conductive material that is arranged on the exterior, interior and/or embedded within a housing around device electronics 602 such that the conductive material contacts the body 601 (e.g., a conductive paint applied to the housing); and/or the shield 603 may comprise a conductive fabric which may, or may not, be attached to a housing around device electronics 602.

In the example of FIG. 6B, sEMG device 620 includes a shield 623 that surrounds device electronics 622 and an sEMG electrode 624, and further includes a conductive ring 625 (shown in cross section) connected to the shield that electrically couples the shield to the body as discussed above in relation to FIG. 5. As a result, the shield 623 attenuates external sources of noise (not pictured) that may couple to aspects of the device electronics 622. In some embodiments, the conductive ring may be a metal ring that extends partially, or completely, around the body 621 of the wearer.

According to some embodiments, shield 623 may include and/or may form part of the housing of sEMG device 620. As non-limiting examples, the shield 623 may comprise a rigid conductor that forms a housing around device electronics 622 and contacts the body 621; the shield 623 may comprise a conductive material that is arranged on the exterior, interior and/or embedded within a housing around device electronics 622 such that the conductive material contacts the body 621 (e.g., a conductive paint applied to the housing); and/or the shield 623 may comprise a conductive fabric which may, or may not, be attached to a housing around device electronics 622.

In the example of FIG. 6C, sEMG device 640 includes a shield 643 that surrounds device electronics 642 and an sEMG electrode 644, and further includes an electrode 646 connected to the shield that electrically couples the shield to the body as discussed above in relation to FIG. 5. As a result, the shield 643 attenuates external sources of noise (not pictured) that may couple to aspects of the device electronics 642. In some embodiments, the electrode 646 may be an auxiliary conductor, which includes a dry sEMG electrode.

According to some embodiments, shield 643 may include and/or may form part of the housing of sEMG device 640. As non-limiting examples, the shield 643 may comprise a rigid conductor that forms a housing around device electronics 642 and contacts the body 641; the shield 643 may comprise a conductive material that is arranged on the exterior, interior and/or embedded within a housing around device electronics 642 such that the conductive material contacts the body 641 (e.g., a conductive paint applied to the housing); and/or the shield 643 may comprise a conductive fabric which may, or may not, be attached to a housing around device electronics 642.

In the example of FIG. 6D, components 662 a and circuit board(s) 662 b of the device electronics are illustrated as separate elements, with conductive traces 662 c of the circuit board 662 b also being illustrated. Illustrative sEMG device 660 includes a shield 663 that covers the device circuit board(s) 662 b and conductive traces 662 c that are routed on the circuit board(s) 662 b. The device 660 also includes an sEMG electrode 664 and an electrode 666 connected to the shield that electrically couples the shield to the body as discussed above in relation to FIG. 5. As a result, the shield 663 attenuates external sources of noise (not pictured) that may couple to the conductive traces 662 c. In some embodiments, the electrode 666 may be an sEMG electrode. As a non-limiting example, the shield 663 may be implemented as a shielding film layer that is laminated onto the circuit board(s) 662 b. In the example of FIG. 6D, therefore, the shield is arranged around part of the device electronics (i.e., the device circuit board 662 b), but may not necessarily be arranged around the components 662 a of the device electronics in order for the shield to attenuate external sources of noise.

Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Further, though advantages of the present invention are indicated, it should be appreciated that not every embodiment of the technology described herein will include every described advantage. Some embodiments may not implement any features described as advantageous herein and in some instances one or more of the described features may be implemented to achieve further embodiments. Accordingly, the foregoing description and drawings are by way of example only.

As used herein, elements referred to as being electrically coupled to one another are arranged such that changes in electrical potential in one element may cause changes in electrical potential in the other element. In this manner, the noise source 510 in the example of FIG. 5 is electrically coupled to the amplifier 520 and to the shield 560. Further, as used herein elements referred to as being electrically connected to one another are arranged so that an electrical conductor directly connects the elements together. For instance, the electrode 545 in the example of FIG. 5 may be electrically connected to the shield 560.

The implementations of DC-coupled amplification circuitry described herein employ discrete analog circuit components. However, it should be appreciated that all or portions of the amplification circuitry and/or associated circuitry in the signal chain may alternatively be implemented using AC-coupled amplification circuitry, one or more application specific integrated circuits (ASICs), and/or any commercial or custom silicon implementation, as embodiments are not limited in this respect. Moreover, it will be appreciated that in some embodiments amplification circuitry may not be included in an sEMG device but rather analog-to-digital converters (ADCs) may directly acquire sEMG signals.

Although the above-discussed examples are discussed in the context of interfaces with EMG sensors, it is understood that the shielding techniques described herein for noise reduction could also be implemented in wearable interfaces with other types of sensors including, but not limited to, electrocardiography (ECG), electroencephalogram (EEG), mechanomyography (MMG) sensors, sonomyography (SMG) sensors, and electrical impedance tomography (EIT) sensors.

Various aspects of the apparatus and techniques described herein may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing description and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 

What is claimed is:
 1. A wearable device comprising: amplification circuitry comprising at least a first differential amplifier; at least two dry sEMG electrodes electrically connected to the amplification circuitry; at least one auxiliary conductor not electrically connected to the amplification circuitry, wherein the at least one auxiliary conductor is configured to be electrically coupled to a wearer of the wearable device; and an electromagnetic shield electrically connected to the at least one auxiliary conductor, wherein the amplification circuitry is positioned between the electromagnetic shield and the at least two dry sEMG electrodes.
 2. The wearable device of claim 1, wherein the electromagnetic shield surrounds at least one input of the first differential amplifier.
 3. The wearable device of claim 1, wherein the electromagnetic shield comprises a metal.
 4. The wearable device of claim 1, wherein the electromagnetic shield comprises a conductive fabric.
 5. The wearable device of claim 1, wherein the electromagnetic shield comprises a conductive paint applied to the at least a portion of the wearable device.
 6. The wearable device of claim 1, wherein the electromagnetic shield comprises a conductive tape.
 7. The wearable device of claim 1, wherein the electromagnetic shield comprises a conductive plastic.
 8. The wearable device of claim 1, wherein the first differential amplifier comprises a field-effect transistor (FET).
 9. The wearable device of claim 1, wherein the first differential amplifier is configured to have an input impedance of at least 1 GΩ.
 10. The wearable device of claim 1, wherein the at least one auxiliary conductor includes one or more sEMG electrodes.
 11. The wearable device of claim 1, wherein the at least one auxiliary conductor includes a conductive cylinder, ring and/or torus.
 12. The wearable device of claim 1, further comprising a housing, and wherein the electromagnetic shield is arranged within the housing.
 13. The wearable device of claim 1, further comprising a housing, and wherein the electromagnetic shield comprises a conductive paint applied to the housing.
 14. The wearable device of claim 1, wherein one or more of the at least two dry sEMG electrodes are configured to pass through at least some portion of the wearer's dermis. 